1. Field of the Invention
The present invention relates to a TDDB (Time Dependent Dielectric Breakdown) test pattern circuit, and more particularly, to a TDDB test pattern circuit which can reduce a test time period and improve a precision of a measurement result statistically; and a method for testing TDDBs of MOS capacitor dielectric films using the same.
2. Background of the Related Art
A related art TDDB test pattern and a method for testing TDDBs of MOS capacitor dielectric films using the same will be explained. FIG. 1 illustrates a unit circuit showing a related art TDDB test pattern circuit, and FIG. 2 illustrates a graph showing an experimental data of TDDB of an MOS capacitor dielectric film measured using FIG. 1.
Referring to FIG. 1, the related art TDDB test pattern circuit includes an MOS capacitor 1 having one electrode grounded and a voltage application electrode 2 for applying a constant voltage Vforce to the other electrode on the MOS capacitor 1. And, there is an ammeter 3 between the MOS capacitor 1 and the voltage application electrode 2 for measuring a current to the MOS capacitor 1.
A related art method for testing the TDDB test pattern circuit will be explained. One side of electrode of the MOS capacitor 1 is grounded, the other side of the electrode is applied of a constant stress voltage of Vforce, and current to the MOS capacitor is measured through the ammeter 3.
FIG. 2 illustrates an example of current to the MOS capacitor along time measured according to the above method, wherein it can be seen that there is a sudden increase of the current time of 340 seconds from an application of the voltage stress to the MOS capacitor 1. This time period of 340 seconds is the Tbd(Time to breakdown) of the MOS capacitor 1. In order to measure a Tbd of each MOS capacitor in N unit test pattern cells according to the test method of the related art TDDB test pattern circuit, a test for each of the N test pattern cells is required, i.e., N tests are required. And, if it is assumed that an average time period taken until an MOS capacitor dielectric film in a unit test pattern cell is Tavg, the total time required for measuring a Tbd of each MOS capacitor dielectric film in N unit test pattern cells is NxTavg.
The related art TDDB test pattern circuit and a method for testing TDDBs of MOS capacitor dielectric films using the same has the following problems.
Significant time period is required for Tbd testing N number of unit test pattern cells, and the use of a testing equipment for a prolonged time period costs high.